Display Device and Manufacturing Method Thereof

ABSTRACT

A display device in which a plurality of gate wires and a plurality of drain wires that intersect the gate wires are provided, and thin film transistors connected to the gate wires and the drain wires are formed for respective pixel regions. At least one of the gate wires, the drain wires, and lead wires drawn from the gate wires or the drain wires is formed of a light-transmitting patterned conductive film. The light-transmitting patterned conductive film is formed of at least a first light-transmitting patterned conductive film, and a second light-transmitting patterned conductive film laminated on the first light-transmitting patterned conductive film. The second light-transmitting patterned conductive film is formed of a conductive film for coating only the surface of the first light-transmitting patterned conductive film including its side wall surface.

CLAIM OF PRIORITY

This application is a divisional application of U.S. application Ser.No. 13/085,517, filed Apr. 13, 2011, the contents of which areincorporated herein by reference.

The present application claims priority from Japanese Patent ApplicationJP 2010-097034 filed on Apr. 20, 2010, the content of which is herebyincorporated by reference into this application.

BACKGROUND

The present invention relates to a display device and a manufacturingmethod thereof, and particularly, to a display device using alight-transmitting conductive film.

Generally, a liquid crystal display device has a microfabricatedelectronic circuit formed on a surface at a liquid crystal side of oneof paired substrates oppositely provided having the liquid crystalinterposed therebetween. A display region (display portion) having aplurality of pixels arranged in matrix, and a peripheral circuit region(peripheral circuit portion) as a peripheral part of the display portionare formed on a surface of the other substrate at the liquid crystalside. The electronic circuits are provided in the display portion andthe peripheral circuit portion.

The electronic circuit in the display portion includes at least athin-film transistor for selecting a group of pixels arranged in rows,and a pixel electrode to which a video signal is supplied through thethin-film transistor. The electronic circuit in the peripheral circuitportion includes a large number of the thin-film transistors forgenerating a signal (scan signal) that drives the thin-film transistorof the display portion, and the video signal.

Each of the electronic circuits in the display portion and theperipheral circuit portion is configured by laminating a patternedconductive film, a semiconductor film, and an insulating film in thisorder. The electronic circuit in the display portion is connected to adrain wire and a gate wire provided in the display region having pixelsformed. The electronic circuit in the peripheral circuit portion isconnected to leading wires which extend from the drain wire and the gatewire in the display region so as to output the video signal and the scansignal to the drain wire and the gate wire via the leading wire. Theelectronic circuit in the peripheral circuit portion is configured toreceive input of the data for displaying from an external device via aterminal portion. The terminal portion is connected to the peripheralcircuit via a wiring (terminal wiring), through which the display datais input to the electronic circuit as disclosed in Japanese UnexaminedPatent Publication Nos. 2006-39509 and 2009-157200.

The liquid crystal display device installed in the portable informationterminal such as a cell phone has been demanded to achieve wide displayregion relative to the limited size of the casing, high-definitionperformance, and high-resolution property. For this, in the generallyemployed liquid crystal display device, the display region is widened byreducing the space occupied by a frame region that is not related to theimage display (that is, narrow frame). Especially in the case where theelectronic circuit in the peripheral circuit portion is not provided inthe frame region, that is, the electronic circuit in the peripheralcircuit portion is formed on the semiconductor chip installed in theterminal portion, the technique is employed for bringing the leadingwire in the frame region into a multi-layer configuration to achieve thenarrow frame, aiming at high-definition and high image quality asdisclosed in Japanese Unexamined Patent Publication Nos. 2006-39509 and2009-157200.

Generally, a metal film (thin metal film) is used for forming theleading wires in the frame region, and the drain and the gate wiresprovided in the display region for suppressing increase in the wiringload. The thin metal film exhibits low corrosion resistance, andaccordingly, the material for forming the wiring layer to be provided atthe position that is likely to be corroded has been demanded. It istherefore preferable to use the light transmitting conductive film suchas ITO (Indium Tin Oxide) with corrosion resistance. However, the sheetresistance of the light-transmitting conductive film such as ITO isstrong. If it is used for forming the wiring, the wiring resistance maybe increased, causing the risk of increase in the wiring load.

When using the ITO with large sheet resistance as wiring, the wiringwidth may be increased. Such structure makes it difficult to realize thenarrow frame. Meanwhile, the film thickness of ITO may also beconsidered. Generally, etching solution of oxalic acid is used afterforming the light-transmitting conductive film as ITO so as to beprocessed into a desired pattern. In the process, the crystalline stateof the light-transmitting conductive film needs to be non-crystalline(amorphous). If the light-transmitting conductive film is crystallized,it cannot be etched by the etching solution of the aforementioned type.When forming the light-transmitting conductive film with large filmthickness, the resultant reaction heat allows easy crystallization. Thisis why the film thickness of the light-transmitting conductive film islimited, resulting in difficulty in formation of the light-transmittingconductive film with the film thickness larger than the predeterminedvalue. The wiring formed using the light-transmitting conductive filmgenerally tends to exhibit relatively large electric resistance.

SUMMARY

The present invention provides the display device which includes wiringsand electrodes each formed of the light-transmitting conductive film forensuring the reduced resistance.

The present invention further provides the manufacturing method of thedisplay device provided with wirings and electrodes each formed of thelight-transmitting conductive film with reduced electric resistancewithout increasing process steps.

(1) The present invention provides a display device in which a pluralityof gate wires and a plurality of drain wires which intersect the gatewires are formed on a substrate, pixel regions are defined by the gatewires and the drain wires, and a thin film transistor connected to thegate wire and the drain wire is formed for each of the pixel regions. Atleast one of the gate wires, the drain wires, and a leading wireextending from the gate wire or the drain wire is formed of alight-transmitting patterned conductive film. The light-transmittingpatterned conductive film is formed of at least a firstlight-transmitting patterned conductive film, and a secondlight-transmitting patterned conductive film laminated on the firstlight-transmitting patterned conductive film. The secondlight-transmitting patterned conductive film is formed of a conductivefilm for coating a surface of the first light-transmitting patternedconductive film including its side wall surface.(2) The preset invention provides a manufacturing method of a displaydevice having a thin film transistors in matrix formed on a substrate,including a first film forming step of forming a first lighttransmitting conductive film on a substrate, a first pattern step ofproviding a first light transmitting patterned conductive film inpatterned crystallized state by subjecting the first light-transmittingconductive film to selective etching through a photolithographytechnique, a second film forming step of forming a secondlight-transmitting conductive film on the substrate, which coats thefirst light-transmitting patterned conductive film, and a second patternstep of providing a second light transmitting patterned conductive filmon the first light-transmitting patterned conductive film inself-alignment by subjecting at least the second light-transmittingconductive film to wet etching.

The present invention provides the light-transmitting conductive filmwith reduced electric resistance without increasing process steps.

Other advantages of the present invention will clearly appear from thefollowing description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view schematically illustrating a structure of a liquidcrystal display device according to an embodiment of the presentinvention;

FIG. 2 is a view illustrating a structure of a pixel in a liquid crystaldisplay device according to an embodiment of the present invention;

FIG. 3 is a sectional view taken along line B-B shown in FIG. 2;

FIG. 4 is an explanatory view showing a manufacturing method of a liquidcrystal display device according to an embodiment of the presentinvention;

FIG. 5 is an explanatory view showing the manufacturing method of aliquid crystal display device according to the embodiment of the presentinvention;

FIG. 6 is an explanatory view showing the manufacturing method of aliquid crystal display device according to the embodiment of the presentinvention;

FIG. 7 is an explanatory view showing the manufacturing method of aliquid crystal display device according to the embodiment of the presentinvention;

FIG. 8 is an explanatory view representing a manufacturing method of theliquid crystal display device according to an embodiment of the presentinvention having a wiring layer formed of a transparent conductive film;

FIG. 9 is an explanatory view representing the manufacturing method ofthe liquid crystal display device according to the embodiment of thepresent invention having a wiring layer formed of a transparentconductive film;

FIG. 10 is an explanatory view representing the manufacturing method ofthe liquid crystal display device according to the embodiment of thepresent invention having a wiring layer formed of a transparentconductive film;

FIG. 11 is an explanatory view representing the manufacturing method ofthe liquid crystal display device according to the embodiment of thepresent invention having a wiring layer formed of a transparentconductive film;

FIG. 12 is an explanatory view representing the manufacturing method ofthe liquid crystal display device according to the embodiment of thepresent invention having a wiring layer formed of a transparentconductive film; and

FIG. 13 is a view illustrating an electric field distribution fordriving the liquid crystal between a pixel electrode and an oppositeelectrode of the liquid crystal display device according to theembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention will be described referring tothe drawings. The same components in the description are designated withthe same reference numerals, and explanations thereof, thus will not berepeatedly described.

General Structure

FIG. 1 is a plan view schematically illustrating a liquid crystaldisplay device according to an embodiment of the present invention. Inthe following description, the present invention is applied to theliquid crystal display device. However, it may be applied to otherdisplay devices such as an organic EL display device without limitation.Codes X and Y denote X-axis and Y-axis, respectively.

Referring to FIG. 1, a liquid crystal (not shown) is interposed betweena first substrate SUB1 and a second substrate SUB2, which are oppositelyarranged. The second substrate SUB2 is designed to face the user. Abacklight (not shown) is provided on a back surface of the firstsubstrate SUB1. The second substrate SUB2 has an area smaller than thatof the first substrate SUB1 so that a lower peripheral portion SD of thefirst substrate SUB1 is exposed. A semiconductor device (chip) SEC isbuilt in the lower peripheral portion SD of the first substrate SUB1.The semiconductor device SEC serves as a control circuit for drivingrespective pixels in a display region AR to be described later. A sealmember SL is provided around the second substrate SUB2, which is bondedto the first substrate SUB1. The seal member SL functions in sealing theliquid crystal.

The region surrounded by the seal member SL is defined as the displayregion AR. On the surface of the display region AR of the firstsubstrate SUB 1 at the liquid crystal side, gate wires GL each extendingalong X direction are aligned in Y direction, and drain wires DL eachextending along Y direction are aligned in X direction. The regiondefined by adjacent paired gate wires GL and adjacent paired drain wiresDL becomes a pixel region. The display region AR includes a large numberof pixels arranged in matrix therein.

Referring to an enlarged part A indicating an equivalent circuit shownin a dotted elliptical frame, each pixel region includes a thin-filmtransistor TFT which is turned ON by a signal (scan signal) from thegate wire GL, a pixel electrode PX to which a signal (video signal) issupplied from the drain wire DL via the thin-film transistor TFT, and anopposite electrode CT for generating electric field between the oppositeelectrode CT and the pixel electrode PX. The electric field has acomponent parallel to the surface of the first substrate SUB1, and theliquid crystal molecules are designed to have the orientational statechanged while being kept horizontal to the surface of the firstsubstrate SUB1. The liquid crystal display device is referred to astransverse field type (IPS type). The opposite electrode CT is designedto receive a reference signal with respect to the video signal via thecommon wire CL which extends parallel to the gate wires GL.

The gate wires GL, the drain wires DL and the common wires CL areconnected to the semiconductor device SEC via corresponding leadingwires (not shown) so that the gate wires GL receive the scan signals,the drain signals DL receive the video signals, and the common wires CLreceive the reference signals, respectively.

The aforementioned structure is shown by taking the liquid crystaldisplay device of so called transverse field type as the example.However, the present invention may be applied to the liquid crystaldisplay device of longitudinal type, for example, TN (Twisted Nematic),VA (Vertical Alignment) and the like.

Pixel Structure

FIG. 2 illustrates the pixel structure of the liquid crystal displaydevice according to an embodiment of the present invention as a planview corresponding to the part A shown in FIG. 1. FIG. 3 is a sectionalview taken along line B-B shown in FIG. 2.

Referring to FIG. 2, a surface of the first substrate SUB1 at the liquidcrystal side, that is, a main surface of the first substrate SUB1 (seeFIG. 3) has a base layer GRL (see FIG. 3) formed thereon. The gate wiresGL each extending along the X direction are aligned in Y direction onthe upper surface of the base layer. Rectangular regions each as thepixel region are defined by those gate wires GL and the drain wires DLeach extending along the Y direction which are aligned in the Xdirection. The gate wire GL is provided with a gate electrode GT formedas a protrusion projecting toward the pixel region. The gate electrodeGT serves as a gate electrode for the thin-film transistor TFT.

Referring to FIG. 3, an insulating film GI which coats the gate wire GL(gate electrode GT) is formed on the surface of the first substrate SUB1on which the gate wires GL are formed. The insulating film GI functionsas a gate insulating film in the region for forming the thin-filmtransistor TFT.

The semiconductor layer (i layer) PS provided while superimposed withthe gate electrode GT in the region for forming the thin-film transistorTFT on the surface of the insulating film GI is formed of a lowtemperature polysilicon (poly-Si) material. Low concentration impuritylayers (LDD layer, n⁻ layer) LDD doped with n-type impurity at lowconcentration are provided at the side of the drain electrode DT and thesource electrode ST of the semiconductor layer PS while interposing thesemiconductor layer PS. The low concentration impurity layer LDDprovides the effect of mitigating field focusing between thesemiconductor layer PS and the gate electrode GT. Contact layers CNLconnected to the source electrode ST or the drain electrode DT areprovided at the side of the drain electrode DT and the source electrodeST of the low concentration impurity layer LDD. The contact layer CNL isa high concentration impurity layer (n⁺ layer) doped with highconcentration n-type impurity. The contact layer CNL provides the effectof reducing the connection resistance between the source electrode ST orthe drain electrode DT, and the channel region. The thin-film transistorTFT does not need to be limited to the coplanar type, but may be ofstaggered type. The gate electrode does not need to be limited to bottomtype, but may be of top gate type.

A first insulating layer IN1 for coating the semiconductor layer PS, thelow concentration impurity layers LDD and the contact layers CNL isformed on the upper surface of the first substrate SUB1. A secondinsulating film IN2 is further formed on the upper surface of the firstinsulating film IN1. Through holes (contact holes) which reach thecontact layers CNL for interposing the semiconductor layer PS are formedin the first insulating film IN1 and the second insulating film IN2. Thedrain electrode DT and the source electrode ST are formed in the throughhole for providing the thin-film transistor TFT. The drain wire DL (notshown) formed of, for example an aluminum thin film, is provided on theupper surface of the second insulating film IN2. The drain wire DL iselectrically coupled with the drain electrode DT. The drain wire DL, thegate wire GL and the gate electrode GT may be formed of ITO film to bedescribed later.

A protective film PAS which coats the drain electrode DT, the sourceelectrode ST and the drain wires DL, and planarizes the surface of thefirst substrate SUB1 is formed on the upper layer of the secondinsulating film IN2. The protective film PAS serves to avoid directcontact with the thin-film transistor TFT, and prevents deterioration incharacteristic of the thin-film transistor TFT. The protective film PAShas, for example a double layer structure, as a body formed bylaminating the protective film formed of an inorganic insulating filmand a protective film (planarized film) formed of an organic insulatingfilm.

A first light-transmission patterned conductive film PX1 formed bypattern etching the light-transmitting conductive film through selectiveetching with a known photolithography technique is formed on the surfaceof the protective film PAS. A second light-transmitting patternedconductive film PX2 which coats the liquid crystal side surface (uppersurface) and the side surface of the first light-transmitting patternedconductive film PX1 is formed. The pixel electrode PX is formed of thefirst light-transmitting patterned conductive film PX1 and the secondlight-transmitting patterned conductive film PX2. The secondlight-transmitting patterned conductive film PX2 is configured to coatthe exposed surface of the first light-transmitting patterned conductivefilm PX1 including its side wall surface. Each of the firstlight-transmitting patterned conductive film PX1 and the secondlight-transmitting patterned conductive film PX2 is formed of acrystallized light-transmitting conductive film as described below.

In the embodiment, the opposite electrode CT is formed of thelight-transmitting conductive film such as ITO (Indium Tin Oxide) overan entire area of the display region AR. A signal (reference signal) asa reference with respect to the video signal is supplied to the oppositeelectrode CT so that the signals are commonly supplied to the respectivepixels. The opposite electrode CT is formed by directly laminating thecommon signal wires CL each formed of metal with low electric resistanceso that the reference signal is supplied to the opposite electrode CTvia the common signal wire CL. The common signal wire CL is formedadjacent or partially superimposed to the gate signal wire GL along therunning direction thereof while avoiding substantial pixel region. Thepresent invention is also applicable to the liquid crystal displaydevice of VA type or TN type having the opposite electrode CT formed onthe second substrate SUB2.

Pixel Producing Method 1

FIGS. 4 to 7 are explanatory views with respect to the manufacturingmethod of the liquid crystal display device according to the embodimentof the present invention. The method for producing the pixel electrodeusing the light-transmitting patterned conductive film according to thepresent invention will be described. The present invention is notlimited to the pixel electrode, but may be applied to the drain wire DLand the gate wire GL each formed of the metal thin film to cope withhigh sheet resistance of the generally employed liquid crystal displaydevice, the leading wiring for connecting those drain wire DL and gatewire GL to outputs of the semiconductor device SEC, and further to theelectrode of the thin film transistor for forming the peripheralcircuit. The manufacturing method according to the present invention isthe same as that for manufacturing the generally employed display deviceexcept the process of producing the pixel electrode formed of thelight-transmitting patterned conductive film. So the method forproducing the pixel electrode formed of the light-transmitting patternedconductive film will be described in detail.

In the process of forming the pixel electrode PX according to theembodiment, the ITO for forming the pixel electrode PX is subjected topattern etching using the known photolithography technique to obtain thefirst light-transmitting patterned conductive film PX1, as shown in FIG.4. In the process of forming the first light-transmitting patternedconductive film PX1, the ITO film ITO is formed on the surface of thefirst substrate SUB1 at the liquid crystal side, that is, the upperlayer of the protective film PAS, and then the etching pattern is formedon the upper surface of the ITO film ITO. For example, the firstlight-transmitting patterned conductive film PX1 along the shape of thepixel electrode PX is formed through wet etching using chemical solutionof oxalic acid. After the etching, the first light-transmittingpatterned conductive film PX1 is in non-crystalline (amorphous) state.It is then subjected to the heat treatment such as the known annealingtreatment to crystallize the etched first light-transmitting patternedconductive film PX1.

Referring to FIG. 5, the ITO film ITO as the light-transmittingconductive film is formed on the liquid-crystal side surface of thefirst substrate SUB1, that is, the upper layer of the protective filmPAS including the upper layer of the first light-transmitting patternedconductive film PX1. If the ITO film ITO is formed to have the thicknessequal to or larger than the predetermined value, the ITO film in contactwith both the upper and side surfaces of the first light-transmittingpatterned conductive film PX1, that is, the exposed surface of the firstlight-transmitting patterned conductive film PX1 is brought into the ITOfilm ITO1 under the reaction heat in the crystallized state.

In the embodiment, the ITO film ITO is subjected to the wet etchingagain using the chemical solution of oxalic acid. The chemical solutionof oxalic acid serves to etch only the ITO film ITO in thenon-crystallized state. As a result, the ITO film ITO1 in thecrystallized state is kept un-etched as illustrated in FIG. 7. Asclearly shown in FIG. 7, the second light-transmitting patternedconductive film PX2 along the shape of the upper and side surfaces ofthe first light-transmitting patterned conductive film PX1 is formed inself-alignment, thus defining the pixel electrode PX. The pixelelectrode PX is formed by laminating the second light-transmittingpatterned conductive film PX2 on the first light-transmitting patternedconductive film PX1, and the resultant thickness is larger than that ofthe generally employed pixel electrode PX. This makes it possible toreduce the electric resistance of the transparent conductive film forforming the pixel electrode PX. Reduction of the electric resistance ofthe pixel electrode PX makes the field distribution within the pixelelectrode PX uniform, thus further making distribution of electric fieldE for driving the liquid crystal between the pixel electrode PX and theopposite electrode CT uniform as shown in FIG. 13. As a result,brightness difference in the same pixel may be significantly reduced.Reduction of the brightness difference in the same pixel is especiallyeffective for the reduced gap between electrodes accompanied withhigh-definition of the liquid crystal display device. This is usable asthe electrode of isotropic crystal demanded by the transverse electricfield type.

In the case where the ITO film ITO formed on the upper layer of thefirst light-transmitting patterned conductive film PX1 has the thicknessequal to or smaller than the predetermined value, crystallization underthe reaction heat resulting from the film-forming process does notoccur. The ITO film ITO1 is thus kept non-crystallized. In this case,the crystallized ITO film ITO may be formed through annealing treatmentusing a laser beam, for example. The wet etching using the chemicalsolution of oxalic acid forms the second light-transmitting patternedconductive film PX2 to be laminated on the first light-transmittingpatterned conductive film PX1, resulting in the aforementioned effect.

Wiring Producing Method

FIGS. 8 to 12 are explanatory views with respect to application of thetransparent conductive film to the wiring layer in the liquid crystaldisplay device according to the embodiment of the present invention. Themanufacturing method and effect resulting from application of thepresent invention to the wiring production will be described referringto FIGS. 8 to 12. In the following description, the wiring layer isformed on the upper surface of the first substrate SUB1. However, thewiring layer may be formed on the upper layer of the second insulatingfilm as the other insulating layer likewise production of the pixelelectrode PX. In the explanation to be described below, a three-layerlight-transmitting patterned conductive film is formed to significantlyreduce the electric resistance of the wiring layer. Like the pixelelectrode PX, the light-transmitting patterned conductive film is notlimited to the three-layer configuration so long as two or more layersare used.

After forming the ITO film on the upper surface (liquid crystal side) ofthe first substrate SUB1, and the wiring mask pattern is formed so thatthe ITO film is wet etched using the chemical solution of oxalic acid.The ITO film ITO2 in non-crystallized state is formed through theetching as shown in FIG. 8. Thereafter, the ITO film ITO2 in thenon-crystallized state is subjected to the heat treatment such asannealing treatment to form a first light-transmitting patternedconductive film ITO3 as the crystallized ITO film.

Referring to FIG. 9, the ITO film ITO is formed on the surface of thefirst substrate SUB1 so that the film thickness becomes equal to orlarger than the predetermined value. Under the reaction heat generatedin the film-forming process step, the ITO film ITO around thecrystallized first light-transmitting patterned conductive film ITO3 isbrought into the crystallized ITO film ITO1 as shown in FIG. 10.

The ITO film ITO is subjected to the wet etching using the chemicalsolution of oxalic acid so that a second light-transmitting patternedconductive film ITO4 as the crystallized ITO film is formed. The secondlight-transmitting patterned conductive film ITO 4 is thelight-transmitting patterned conductive film having only thecrystallized ITO film ITO1 kept un-etched as shown in FIG. 10. Thesecond light-transmitting patterned conductive film ITO4 may be formedin self-alignment along the shape of the upper and side surfaces of thefirst light-transmitting patterned conductive film ITO3 without usingthe photolithography technique.

The ITO film is formed on the upper surface of the first substrate SUB1that contains the second light-transmitting patterned conductive filmITO4 again so that the upper and the side surfaces of the secondlight-transmitting patterned conductive film ITO4 are crystallized underthe reaction heat as described above. The ITO film is subjected to thewet etching using the chemical solution of oxalic acid to etch thenon-crystallized ITO film ITO. This makes it possible to form a thirdlight-transmitting patterned conductive film ITO5 in crystallized statein self-alignment. In this way, the wiring layer is formed of athree-layer light-transmitting patterned conductive film including ITO3,ITO4 and ITO5. The resultant wiring layer is capable of reducing theelectric resistance to the degree greater than the wiring layer formedof a single layer of the light-transmitting patterned conductive film.

As described above, in the liquid crystal display device according tothe embodiment of the present invention, the first light-transmittingpatterned conductive film is formed on the surface at the liquid crystalside of the first substrate SUB1. The first light-transmitting patternedconductive film is subjected to selective etching through thephotolithography technique so as to form the patterned crystallizedfirst light-transmitting patterned conductive film. The secondlight-transmitting patterned conductive film is formed to coat the firstlight-transmitting patterned conductive film, and is at least furthersubjected to the wet etching so as to be formed on the firstlight-transmitting patterned conductive film in self-alignment. Thelight-transmitting patterned conductive layers may be easily laminatedafter forming the first light-transmitting patterned conductive filmwithout using the photolithography technique, that is, withoutincreasing process steps. As a result, the electric resistance of thelight-transmitting patterned conductive film may be significantlyreduced. This makes it possible to easily use the light-transmittingpatterned conductive film for forming the wiring layer which has beenconventionally formed of the metal thin film. The light-transmittingpatterned conductive layer may be formed of a plurality of filmsincluding the first, second and third light-transmitting patternedconductive films so as to increase the pattern width of thelight-transmitting patterned conductive film, thus further reducing theelectric resistance.

The present invention has been described in specific way in reference toan embodiment. It is to be clearly understood that the invention is notlimited to the above-described embodiment, but may be subjected tovarious modifications without departing from the scope of the presentinvention.

What is claimed is:
 1. A display device in which a plurality of gatewires and a plurality of drain wires which intersect the gate wires areformed on a substrate, pixel regions are defined by the gate wires andthe drain wires, and a thin film transistor connected to the gate wireand the drain wire is formed for each of the pixel regions, wherein atleast one of the gate wires, the drain wires, and a leading wireextending from the gate wire or the drain wire is formed of alight-transmitting patterned conductive film; the light-transmittingpatterned conductive film is formed of at least a firstlight-transmitting patterned conductive film, and a secondlight-transmitting patterned conductive film laminated on the firstlight-transmitting patterned conductive film; and the secondlight-transmitting patterned conductive film coats a surface of thefirst light-transmitting patterned conductive film including its sidewall surface.
 2. The display device according to claim 1, wherein eachof the first light-transmitting patterned conductive film and the secondlight-transmitting patterned conductive layer is formed of acrystallized conductive film.
 3. The display device according to claim1, wherein the second light-transmitting patterned conductive film has asection orthogonal to an extending direction larger than a width of thefirst light-transmitting patterned conductive film.
 4. The displaydevice according to claim 2, wherein the second light-transmittingpatterned conductive film has a section orthogonal to an extendingdirection larger than a width of the first light-transmitting patternedconductive film.
 5. The display device according to claim 1, wherein thefirst light-transmitting patterned conductive film is formed on and inphysical contact with a insulating film, the second light-transmittingpatterned conductive film is not in physical contact with the insulatingfilm.
 6. The display device according to claim 5, wherein the insulatingfilm coats a source electrode and a drain electrode of the thin filmtransistor.
 7. The display device according to claim 5, wherein theinsulating film is an organic insulating film.
 8. The display deviceaccording to claim 2, wherein the first light-transmitting patternedconductive film is formed on and in physical contact with a insulatingfilm, the second light-transmitting patterned conductive film is not inphysical contact with the insulating film.
 9. The display deviceaccording to claim 8, wherein the insulating film coats a sourceelectrode and a drain electrode of the thin film transistor.
 10. Thedisplay device according to claim 8, wherein the insulating film is anorganic insulating film.